We have developed an in vitro system that synthesizes infectious bacteriophage phiX174 particles. The synthesis of phage particles is coupled with de novo synthesis of circular single-stranded (S-S) viral DNA. The system depends on the presence of phage coded proteins A, B, C, D, F, G and H. We plan to analyze biochemical functions of these proteins during S-S synthesis and phage maturation. We have already purified B protein containing prohead which is an essential component of the system. Using a similar approach, we will be able to purify the other protein components which are needed for in vitro activity.